Do you have tested with only one loop?
The ToolTip property holds the Text you are setting to it
Get the amount of memory each time you set the property and see the increase, if it is constant, that is the size the Tooltip property needs to hold the string you set. off course there are hidden data structures than VFP uses to do its things and many times you can obtain the needed memory.
Is like the hard disk storage there are clusters (4 Kb for FAT 32) but a file with 100 bytes use one cluster (4Kb). Maybe the OS is allocating more memory htan it need.
I think so

Mauricio