Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Manufacturer | Type | Quantity | PTRD Nos. | GWR Nos. |
| --- | --- | --- | --- | --- |
| Robert Stephenson & Co. | 0-6-2T | 7.0 | 8–14 | 183–187 |
| Hudswell Clarke | 0-6-0ST | 6.0 | 22–27 | 808–809, 811–814 |
| Robert Stephenson & Co. | 0-6-0ST | 2.0 | 3, 15 | 815, 816 |
| Sharp, Stewart & Co. | 2-4-0T | 1.0 | 37 | 1189 |
| Sharp, Stewart & Co. | 2-4-2T | 1.0 | 36 | 1326 |
| Sharp, Stewart & Co. | 0-8-2T | 3.0 | 17–19 | 1358–1360 |
| Cooke Locomotive & Machine Works | 0-8-2T | 2.0 | 20–21 | 1378–1379 |
Question:
What is the highest Quantity for PTRD Nos. 3, 15?
Answer:
2.0