Jose
I would first increase the memory_limit and monitor what is happening. You may have enough sqt cache and everything will be fine.
If you are also seeing warning messages similar to this:
W. 2014/04/20 19:12:46. WARNING #24068 SQT(103:1 DIST PDS.pdb) - t/sqtint.c(1380) SQT cache size is too low to load more than one transaction into the cache.
or
W. 14/04/20 18:12:46. WARNING #24057: _sqt_remove_largest_tran(252:1 PDS.pdb): No candidate found for removal. Memory limit will be exceeded by SQM/TI thread.
then you would need to increase your sqt cache size after you increased your memory_limit.
Regards
Terry