Depends on how much I see myself playing the game in the future. WoW Subscription was a no brainer for 10+ years for example.
In general, I don't spend money on a game unless it directly affects my ability to play that game. Like SWTOR, I only play when I want to drop some money on a subscription, since playing for free limits what gear I can use and how much money I can spend.
Online mobile games? Idk if I'd ever spend a dime. It's on my phone so I wouldn't value it very highly, and I'd probably get bored of the app and uninstall it within a month to a week. If you spend a lot of time playing mobile games I'd say go for it.
Look at it this way, going to the movies (alone rip.) is $15-30 canadian depending if you went on tuesday or not. Something like that right? That's for 1-2 maybe 3 hours of your time. How long will your $15 payment last you in the mobile game? Longer than 2-3 hours? What's your entertainment worth to you?