Ok, not sure if you're having trouble finding 15/10 or figuring out how to play with your friend. To find 15/10: roll your cursor over to home (upper right) and click on live chess. Click on "play now" and that brings you to the live server. Now, right next to the "1 minute" is a little upside down triangle. That's a roll up ( or down) menu. Click on the triangle and you should find 15/10 among the options.
You probably already know all that and want to know how to challenge your friend. Let me get a link for you that explains it better than I could. The important thing is you both have to be logged into the live server. Live is in the second part of the article.
https://support.chess.com/customer/portal/articles/1444882
Enjoy!
Dear friends! I would like to play with my amogo in format 15/10 we are could not to find option on the site!!! Please, Help!