Fairway Solitaire is a very large app because it has nearly 1000 unique holes to play. Because of that, many devices get bogged down over time. I find that if you shut off your device completely and turn it back on, many of the sluggishness or crashing is solved.
Also, just as Apple recommends with any app, remember to back-up your data to iCloud often. Fairway Solitaire saves data locally (to your device) and not to the cloud yet. The developer, Big Fish Studios, said that they are building the game to save to the cloud, but that hasn't been implemented at this time.
If you do not back-up your data via iCloud, you may lose all progress, golf bucks, stars, cups, trophies, and records if the app or the device resets itself.