You probably won't like this answer, but the way to get faster at reading sheet music is to read sheet music. It's a skill and takes time and consistent practice to develop.
Sight-reading exercises are great for improving, but it seems you are struggling to choose an appropriate difficulty. A piano teacher is very helpful in this regard and can recommend books/exercises for you to work through.
If that's not an option for you, there are piano music grading systems that provide some orientation. For example IMSLP[1] has music by level, according to the Royal School of Music.
Disclaimer: I'm not an avid piano player, so I don't know that much about these grading systems, other than they are used for exam and certificate prep.
Sight-reading exercises are great for improving, but it seems you are struggling to choose an appropriate difficulty. A piano teacher is very helpful in this regard and can recommend books/exercises for you to work through.
If that's not an option for you, there are piano music grading systems that provide some orientation. For example IMSLP[1] has music by level, according to the Royal School of Music.
Disclaimer: I'm not an avid piano player, so I don't know that much about these grading systems, other than they are used for exam and certificate prep.
[1]: https://imslp.org/wiki/Special:DiffPage/DiffMain/1