Yes this is an issue, when you have many textures all tiled. Depending on your vray version, if you are in vray 3, you may try option - cache bitmaps between renders. This will keep the textures in ram on the same mayabatch job I believe. If you are in vray 2.x you need to declare this variable for the same result:
SET VRAY_MAYA_KEEP_BITMAPS=1