Check your Dcadwin.ini file for these settings
[Bitmaps]
MinSize=0.001
MaxSize=100
; Specify the minimum and maximum size in megabytes of bitmaps to store in memory.
; Increase the minimum size and decrease the maximum size if the amount of RAM you have available is limited (i.e. 256MB or less) and if your drawings contain either a lot of and/or large bitmaps.
my settings are
[Bitmaps]
MaxSize=0.005
MinSize=0.001
See more all the settings at:
https://www.datacad.com/ddn/dcadwin.ini.html