Stay Up Late works with more than 100 people with learning disabilities and autistic people, and has over 100 volunteers.
It campaigns for equality, wanting to make sure its people are able to have active social lives, full of the things that matter to them.
This means: Choosing how they spend their time and what their lives look like; not having their evenings cut short because of inflexible rotas for support staff, blanket curfews or residential homes locking their doors at 10pm and having the freedom to see friends and build connections with their community.
Katie Windsor, Director of Stay Up Late, which has HQ in Hove, said: "It has been a remarkable 15 years, and I am proud that we have achieved so much in that time.
“People with learning disabilities and autistic people are too often shut out of social life by inaccessible venues, attitudes and systems. We work to break those barriers down, so everyone can enjoy the things that a lot of us may take for granted.
"We held a celebration party at Daltons in Brighton to mark our anniversary, and we intend to carry on making a difference for the next 15 years and beyond. We believe that having the choice to stay up late matters - and that is our key message.
"Part of our work is campaigning, the other part is our Gig Buddies project where we pair one of our participants with a volunteer Buddy. They go out together a minimum of once a month, and over time genuine friendships flourish.
"After a while, some may leave us but that's because they have created a natural friendship, and that's a success for us."
The charity covers the whole of Sussex, although its main focus is currently around Brighton and Hove, Adur and Worthing areas.
Fancy becoming a Buddy? Go to www.gigbuddies.org.uk/be-a-gig-buddies-volunteer
To find out more, email [email protected].

1. Sussex charity celebrates 15 years
Sussex charity celebrates 15 years Photo: supplied

2. Sussex charity celebrates 15 years
Sussex charity celebrates 15 years Photo: supplied

3. Sussex charity celebrates 15 years
Abigail and Emma. Photo: supplied

4. Sussex charity celebrates 15 years
Jay and Joe Photo: supplied