[Android Q&A, Help & Troubleshooting] francwalter:
This HowTo is for Cat beginners who want to root their phone and didn't understand the first post like me :)

You need a bit of knowledge about your phone, what root means, what flashing means, some little more than beginners skills on computers at least. If things like "adb" are really unknown, try to read a bit about it first.

The HowTo in the first post here it was not enough information for me, but with the very big help of Cat-Guru "harddisk_wp" (by online chat and TeamViewer) I got my friends Cat B15Q rooted :)

So I wrote this little more detailed HowTo for beginners in my level.

But anyway you should first read the first post!

What you need:

You need a Windows PC with 32 Bit System (e.g. XP or 7), as the 64 Bit System won't allow you to install an unsigned driver and the MediaTek Drivers are unsigned.

I did it successfully with an old Windows XP Home/Pro (a home with some pro features, but real home or pro will do it) 32 Bit, SP3. Windows 7-64 or 8/8.1 won't work.

You need the MediaTek drivers (MTKUsbAll_0.9.2.rar, Download from first post links)

You need the SP Flash Tool (SP_Flash_Tool_v5.1352.01, Download from first and fourth post links)

You need the scatterfile for the Cat B15Q (MT6582_Android_scatter.txt, Download from first post links)

You need the CWM Recovery file (USBFIX RECOVERY CWM.img, Download from first post links)

You need the SuperSU file (UPDATE-SuperSU-v2.46.zip don't unzip, Download from http://download.chainfire.eu/696/SuperSU/UPDATE-SuperSU-v2.46.zip )

You could need the USBFIX boot (USBFIX boot.img) to easier install the adb driver

Your Cat need to have USB-Debugging enabled (for the adb connection later)

Start SP Tool

Remove the Battery from the Cat phone (leave it away)

Put the USB kable from Cat to PC, you will hear again and again the ding dong sound of USB plugged in and out. The Driver Installer Assistant will open (hopefully).

Install the "MediaTek Preloader" driver by choosing the driver folder by yourself, choose the folder "New inst. win 7&8x64", from the drivers package,

accept it and just click OK, when there is a box with three different drivers (Screenshot: mtk-preloader-driver.jpg), just don't change it and take the first.

Important to accept the unsigned driver, even when Windows warn not to do it (Screenshot: mtk-driver-warning.jpg).

The ding-dong-sound will continue even when the driver is installed. The sound will only stop for the time the SP Tool is at work! This irritated me first.

First we make a backup of the whole system:

Here fore open the SPTool and under the Tab "Readback" click on the 'Read Back' Button.

now the Dingdong stops and a line fills in the list.

Now click into this filled line and save under boot.img. Put start value

0x5980000

and end value

0x1000000

both hex then hit OK.

Maybe you have to drag the table column a bit to see the whole value. You can double click the cols edge to auto fit.

Now with 'Add' Button make a new line and one after the other fill in like before these values and save them:

this was the first line, which you already filled with:

boot.img (save as)

0x5980000 (start value)

0x1000000 (end value)

2. line

recovery.img

0x6980000

0x1000000

3. line

system.img

0x9800000

0x50000000

4. line

userdata.img

0x69800000

0x7BF20000

Info: All these start and end values are obtained from the scatterfile, you can see them also in the "Begin Address" and "End Address" columns in the "Download" Tab of SP Tools (when you have loaded the scatterfile),

where "BOOTIMG" > boot.img, "RECOVERY" > recovery.img, system.img > "ANDROID" and "USRDATA" is the userdata.img

Now remove the USB cable, click the 'Read back' Button and put the cable back in.

Now the SP Tool reads the whole ROM which took me on my old XP Medion Netbook nearly 2 hours!

The file "system.img" was about 1.3 GB big, "userdata.img" about 2 GB.

Info: the start and ending values come from the scatterfile which was obtained with the MTKDroidTool (the inofficial MediaTek Tool like e.g. Odin for Samsung).

As the scatterfile can just be downloaded, no need to use the MTKDroidTool.

Now you have the backup, whith this you could restore the system if something goes wrong by flashing the CWM (to get root).

Flashing the CWM Recovery:

In the "Download" Tab load the scatterfile to the "Scatter-loading File" field, click the 'Scatter-loading' Button to load the file.

The table is now filled with 12 lines of all the partitions (Screenshot: sp_flashtool.jpg and sp_flashtool2.jpg).

Click into the "Location" field in the "RECOVERY" line ("RECOVERY" you find in the "Name" column) and select the file "USBFIX RECOVERY CWM.img" from where you saved it.

Now remove again the USB cable, click 'Download' button and put in the cable.

The CWM Recovery is fastly flashed, some seconds only.

Now you can flash also the USBFIX boot.img, which makes it easier to install the adb driver, put the file to "BOOTIMG" line and flash it like before

(pull out cable, press 'Download', put in cable).

This is also fast done.

Installing the SuperSU app:

If not yet done, install adb on your computer, you can download the installer from:

http://download.clockworkmod.com/test/UniversalAdbDriverSetup.msi

Install also on your pc the universal adb drivers from:

https://drive.google.com/file/d/0B1S0LCuXCnnmOWhnUk1ZWVdQakE/view?usp=sharing

Put in the battery, boot to Android and put in the cable.

Let the adb drivers install, they should install automatically (if not, see above "Without adb:")

Now you should be able to connect your Cat with your pc using adb. Open adb on the command line prompt and write:

adb reboot recovery

(your Cat should now switch off and start into recovery mode, there should be written "rua1 autoCWM v5.5.0.4 for B15Q" and at the bottom something like: "CWM automade 31.12.2014 17:25:42")

Move the SuperSU file ("UPDATE-SuperSU-v2.46.zip") into the adb-directory (where your adb.exe is located)

Write to the commandline:

adb push UPDATE-SuperSU-v2.46.zip /sdcard/supersu.zip

(this copies the SuperSU file to the sdcard of the Cat)

Now you can use the recovery to flash the SuperSU file (the "UPDATE-SuperSU-v2.46.zip") using the "install zip file" command from recovery.

After reboot the SuperSU should be there.

If not, try again to flash it in recovery, sometimes only after the second flash process it works.

You should have root now and you should be able to use SDFix ore similar apps to fix the Google Kitkat Superbug of unwritable external SD-Card :)

You can now use FolderMount to use the external sd-card for folders with big data like e.g. WhatsApp.

You can now use Link2SD to use your external sd-card for apps, instead the very small internal sd-card. You need a Linux file-system partition on your external sd-card for it to work (can be done with free tools on windows).

With both, Link2SD and FolderMount your internal 2 GB are absolutely sufficient for the system and its apps, which only remains on the internal sd.

Without adb:

adb makes it easier but is not absolutely needed.

If you are not able to install the adb driver, than you can also take out the SD-Card, copy the SuperSU file on it through your computer and put it back into the phone.

Enter the recovery mode by: press power + volup for 2 seconds, then release power, release volup as soon as recovery has booted

Flash the SuperSU file in the recovery as described before. Maybe twice, best without booting into Android after flashing the fist time.

This is the same result as with pushing the file with adb to the sd-card and flashing it in recovery.

Feel free to ask if there is something unclear.

I wish you success!

EDIT 2015-04-21: when I first tried to install the adb-drivers (only adb, the other drivers wont install on 8.1-64!!!) on my Windows 8.1 (64) machine I needed to change the Android default USB driver package, the inf-file didn't have the VID/PID-code of the Cat.

So I added this info at two positions into the inf-file and voila I could install it, this worked.

This is the code I added in the inf-file:

[Google.NTx86]
...
; Cat B15Q MT65xx
%SingleAdbInterface% = USB_Install, USB\VID_04B7&PID_88AA
%CompositeAdbInterface% = USB_Install, USB\VID_04B7&PID_88AA&MI_01
%SingleBootLoaderInterface% = USB_Install, USB\VID_04B7&PID_88AA
[Google.NTamd64]
...
; Cat B15Q MT65xx
%SingleAdbInterface% = USB_Install, USB\VID_04B7&PID_88AA
%CompositeAdbInterface% = USB_Install, USB\VID_04B7&PID_88AA&MI_01
%SingleBootLoaderInterface% = USB_Install, USB\VID_04B7&PID_88AA
...

I added a zipfile containing only the changed file android_winusb.inf as well.

EDIT 2017-03-30: it is not neccessary to use a 32-Bit PC, it is enough to use a 32-Bit virtual machine in vmware, e.g. Windows XP. I just flashed TWRP 3.0 with this.