Here are some guidelines for the maximum supported number of products and variants by iPad type. Anything above these figures may well work, but we don't give any guarantees:
iPad 2: 2000 products, 4000 variants
iPad 3: 3000 products, 6000 variants
iPad Air: 5000 products, 8000 variants
Also, It's always a good idea to remove any unwanted apps and products to increase the POS app's performance.
Hope that helps!