Use the -start_number
option for the image2 muxer. From the documentation:
-start_number
Start the sequence from the specified number. Default value is 1. Must be a non-negative number.
Your command would then look like:
wine avs2yuv.exe input2.avs - | ffmpeg -y -f yuv4mpegpipe -i - \ -vf fps=fps=15 -q:v 2 -start_number 1501 ./thumb002/%09d.jpg