There are a couple of ways to attack this probably.
1. Don't monitor all interfaces. Now this is way easier said then done. Comparing Spectrum to UIM is like comparing apples to oranges but Spectrum does a great job identify upstream interfaces and in turn makes it really easy to only monitor those interfaces. UIM is not as mature as Spectrum in this space at the moment so you have to try to use the template filters to try to get the job done.
2. Adjust the data retention for those particular QOS tables. If you are storing less raw data then your table will shrink. You have to determine what is the absolute minimum amount of interface raw data you can live with.
Something else you could also look into is how many days worth of data do you have in those tables. If you are using data_engine to perform your data-rollup it is worth taking a look at. I work for a MSP and we have a TON of data. What we found is that the data-rollup job was failing when it hit the interface data tables. By the time we caught it we had at least double the days worth of data as what we set in our retention period. Hopefully that isnt your issue but that is something to look for.