Allison H. answered 06/22/19
Private Piano Instructor
It can be easier to compose music you are capable of playing yourself but is not a requirement. A strong understanding of the instrument is more of a prerequisite than ability. For example: orchestral composers utilize instruments that they do not personally play though they have a thorough understanding of those instruments (range, capabilities, tone color, etc.).
I would recommend composing using software like MuseScore (which is free). This allows you to listen to the music you compose and adjust the tempo. That way you can hear it without trying to play it yourself and see if you like the sound at a faster tempo. If you have a generous pianist friend they might be able to play it for you as well.