How to keep these crickets alive?

Not to be rude, but you should have prepared a place where the crickets could've stayed in advance. Keep in mind, that they are escape artists, and are really fast therefore, hard to catch.

Like u mentioned, apples are great. They provide the proper moisture and nutrients for them. I think a small slice of it will sustain your 15 small crickets for a day. Just replace it with a fresh one daily. Cuz the apples will dry out.

You could also use nearly anything else that u can find in your household.

Veggies, fruit, and more.

If you are feeding the crickets to a pet, then try feeding more nutritious things to them. This is called "gutloading."

Do not put your crickets outside, it is likely too cold or hot. I learned the hard way, all my 50 crickets (medium) I bought died because I left them outside. :'(

Put them in a container with many small air holes. Any container that they cannot climb out of is fine.

Hope this helped! :)

Throwing a damp piece of carrot or other veg in the holding box will keep them aliv3e for three days. If you want them to last longer you'l;l need to set them upv properly in a box with air holes and a tight fitting lid - storage cointainers are ideal.