We did not convert to tsi1, it solved our problem while still using inmem. High series cardinality can use up a lot of memory, but you seem to have plenty of memory on your instance. Also, if unbounded queries are being made by users via either http or Grafana (or similar), it can also cause high memory usage. There are config settings to control that.
If you have a lot of ephemeral data, then trying tsi1 may solve your issue, but I would test it out first, since converting back to inmem can be problematic.
