GIF Question

Ok so I have a GIF that I got online that's 2 seconds and I was wondering if anyone could help me find or anyone that knows any iOS App that can make the GIF longer than it is. I'd like to make it about 15 seconds long.
I do not want to download photoshop or any other program and create them myself because I have no knowledge in using GIF with that.
Is there any program where I can upload the picture frames and let it duplicate itself over and over to a point where it reaches 15 seconds?
I've tried doing it by hand and it would take forever lmao.

Lol if you had photoshop this is literally like a 2 minute job.

I don't know anything about the iOS marketplace though, sorry.

The only easy way would be to do it in Photoshop.

Thanks for the help, I'll just look on youtube on how to do it on photoshop then.