On July 17, 2015, MBK Entertainment announced that T-ara would be part of their summer performance lineup in the first week of August. In August, T-ara's made their seventh extended play (EP), with the title "So Good". The title was track "So Crazy". The EP was composed by Brave Brothers.
In October 2015, the website "Insider Monkey" published a list of 16 best selling girl groups of all time. T-ara was number ten on the list with a total of 36.18 million sales. Later in the month T-ara appeared on the Chinese variety show "The Brain".
In June 2016, T-ara performed at the "Dream Concert 2016", with a remix of "Be Peep Bo Peep", "Roly Poly", and "So Crazy".
On September 9, T-ara performed 3 songs for the IASGO in Seoul. Then on September 11, T-ara flew to Japan for a concert at the Tokyo Dome City Hall. T-ara performed seven songs and talked to their fans. T-ara performed twice during the day, as the event was divided into 2 parts. One was in the afternoon and the other in the evening. At this concert T-ara performed their song "Memories" live for the first time. On September 17, T-ara held their last Concert in the Great China Tour at the Mercedes-Benz Arena in Shanghai. Also in September 2016, the Dong-a Ilbo newspaper listed "Roly-Poly" as the 14th favorite song of the past 20 years.
On October 1, 2016, T-ara performed at the Busan One Asia Festival. They also held a concert on October 4 and performed eight different songs.
T-ara flew to Jeju for a concert the next day, and performed five songs.
In November 2016, T-ara made their eighth extended play (EP), with the title "Remember". The lead single of the EP was "Tiamo". Their music video for "Tiamo" was voted the number one music video of the year on Fuse.
In February 2017, Hwayoung and her twin sister Hyoyoung spoke about the "bullying" scandal on a reality show. Hwayoung used the opportunity to state how hard it was for her, and her only support was her sister. This brought the rumors back to public attention. Soon after, a former staff member claimed that it had really been the twins who had "bullied" the other members. This person released texts that appeared to show Hyoyoung threatening Areum with physical harm. Other staff members also came forward with evidence that Hwayoung had treated the other members and staff badly. They also claimed that she had faked how severe her injury was, in order to get more sympathy. Hwayoung at first tried to deny this, but later admitted that the texts were real. This put an end to the bullying rumors about other members of T-ara.
In March 2017, MBK Entertainment announced Soyeon and Boram were ending their contracts in a few months time. They also stated that T-ara would make one more album as a six member group. However, a conflict with their management lead to a delay and it did not happen. Instead, the release was rescheduled for after Soyeon and Boram had departed. T-ara's last performance as six-member group was in Taiwan on May 13, 2017.
T-ara made their ninth extended play (EP) as a four member group, with Qri, Hyomin, Jiyeon, and Eunjung. The title is "What's My Name?" and it was released on June 14, 2017. T-ara won first place on "The Show" on June 20. This was their first win on a music show in five years.
In July 2017, T-ara made the song "My Love" for the television drama "Greatest One-Shot".
On November 4, the group held a concert in Ho Chi Minh City, Vietnam. Part of the ticket proceeds were donated to charity. On November 24, the group performed with B.A.P, Rain, Kim Jong-kook and Haha for K-Pop Music Wave 2017 in Penang, Malaysia.
On January 3, 2018, Hyomin announced that she, Jiyeon, Eunjung, and Qri would not renew their contracts with MBK Entertainment. The record label later confirmed that the group had left the company. MBK later confirmed that they had filed for a trademark on the name "T-ara". In January 2018, Hyomin, Jiyeon, Eunjung, and Qri filed for a rejection of MBK's trademark request. In August 2018, MBK's trademark request was denied. This allows Hyomin, Jiyeon, Eunjung, and Qri to continue using the group name. They later stated that they intend to stay together as a group.
In an interview in October 2019, Jiyeon stated that they hope to appear again as group. However, she also said that it may not be right away but only after some time passed.
Jiae and Jiwon left the group in 2009, before their official debut. Boram, Qri, and Soyeon were added soon after, and before the official debut. Hwayoung joined the group on July 26, 2010. Areum joined T-ara in early 2012.
Hwayoung had her contract ended in mid-2012 and had to leave the group. Then Areum left in July 2012. T-ara continued as a six-member group until Soyeon and Boram left in 2017. The remaining four members are Qri, Hyomin, Jiyeon, and Eunjung.
On several occasions T-ara formed sub-groups (or sub-units). These were smaller girl groups formed with a few members of T-ara. The first sub-groups of T-ara were formed in March 2013 when "Bunny Style!" was released. These made a few of the songs that were included with "Bunny Style!" in special editions. As these groups had no activity apart from T-ara, they had no official names. The first official sub-groups came a few months later.
On April 12, 2013, Core Contents Media announced a sub-group called T-ara N4. The members were Jiyeon, Eunjung, Hyomin, and Areum. The group's first song, "Jeon Won Diary", was inspired by a 1980s drama show. It is a "funky and intense" dance song with elements of hip-hop. T-ara N4 released the song, the extended play (EP) of the same name, and a music video on April 29, 2013.
A Japanese sub-group called QBS was announced in May 2013. The members were Qri, Boram and Soyeon. QBS focused on the Japanese market. They released their first single "Kaze no You ni" on June 26, 2013. It was written and composed by Takanori Fukuta. QBS held a live show at the Sunshine City Fountain Square in Ikebukuro, Tokyo on June 10, 2013. At the show the group performed "Kaze no Yō ni". Boram and Qri also sang their song "Shabontama no Yukue" and Soyeon sang her song "Love Poem".
In October 2009, the group signed a contract to make a commercial for Nonghyup Apples. They made the song "Apple Song" for the commercial. It was later included on the group's first studio album "Absolute First Album" under the name "Apple is A". In 2010, the group modeled for Mentholatum Korea, Tedin Water Parks, and Olympus cameras. T-ara was chosen to model for Tedin Waterpark again in 2011.
In 2011, T-ara starred in commercials for Spris, iRiver, Windysoft, Look Optical, Shin Ramyun, and Crown Mountain. T-ara also launched the café franchise called Cafe Page One. The name was taken from the cafe that Eunjung's character ran in the drama "Coffee House". When it was opened on July 1, 2011, the members of T-ara were present to greet the customers. The same year, T-ara was chosen as models for cosmetics brand Tony Moly. The group modeled for the brand in South Korea, China, Japan, and other Asian countries. T-ara also signed a contract with online shopping mall Hi-Mart.
In February 2012, T-ara became models for the chicken franchise Brilliant Chicken.
In early 2015, T-ara signed a USD 1 million contract with the Chinese clothing brand Celucasn. In November, T-ara made a Chinese version of "Cry Cry" to be the theme song for the game "World of Warships". The group also became the face of the mobile game "Dream of the Three Kingdoms". In the same month, T-ara was made brand ambassadors of the partnership between Hankyung Media Group and Sina Weibo.
In 2016, the group became brand ambassadors in Vietnam for Pantech Korea.