Cordova/PhoneGap applications are known to eat a lot of memory.
Cordova + Ionic is sometimes ever worse match: Probably, but it doesn’t explain why Cordova with Ionic uses way much more memory than Cordova alone.
For example take a look at this forum post:
It is also possible you have a problem with a memory leak. I can’t see your code so I can’t tell you if this is the case. Not to mention Cordova plugins which can also be a cause for memory leaks.