Problems building Image slideshow with sliding tra

I'm trying to create image slideshow with slide transition using ffmpeg and the following command:

ffmpeg -loop 1 -i img1.jpg -loop 1 -i img2.jpg -loop 1 -i img3.jpg ^
-filter_complex ^
"nullsrc=size=800x600[v0]; ^
[0:v]trim=duration=5,scale=800x600,setpts=PTS-STARTPTS[v1]; ^
[1:v]trim=duration=5,scale=800x600,setpts=PTS-STARTPTS[v2]; ^
[2:v]trim=duration=5,scale=800x600,setpts=PTS-STARTPTS[v3]; ^
[v0][v1]overlay=x='min(-w+(t*w/0.5)\,0)':shortest=1[vv0]; ^
[v1][v2]overlay=x='min(-w+(t*w/0.5)\,0)':shortest=1[vv1]; ^
[v2][v3]overlay=x='min(-w+(t*w/0.5)\,0)':shortest=1[vv2]; ^
[vv0][vv1][vv2]concat=n=3:v=1:a=0 [video]" -map "[video]" output.mp4

I want every image to slide in from left for 0.5 seconds and stay for further 4.5 seconds, before it's being overlapped by the next one and so on.

First problem is that it takes 2-3 minutes to build video with just 3 images and I want to add more images which will result in extremely long build time.

Second problem is that video should be 15 seconds long, but it's only 8 as first image is shown for 5 seconds, second is shown for 2 and the last one just for 1 second.

Your help will be greatly appreciated.

An input pad generated inside a filter complex can be used only once. So, you should split those streams which will be reused.

ffmpeg -loop 1 -i img1.jpg -loop 1 -i img2.jpg -loop 1 -i img3.jpg ^
-filter_complex ^
"nullsrc=size=800x600[v0]; ^
[0:v]trim=duration=5,scale=800x600,setpts=PTS-STARTPTS,split[v1a][v1b]; ^
[1:v]trim=duration=5,scale=800x600,setpts=PTS-STARTPTS,split[v2a][v2b]; ^
[2:v]trim=duration=5,scale=800x600,setpts=PTS-STARTPTS[v3]; ^
[v0][v1a]overlay=x='min(-w+(t*w/0.5)\,0)':shortest=1[vv0]; ^
[v1b][v2a]overlay=x='min(-w+(t*w/0.5)\,0)':shortest=1[vv1]; ^
[v2b][v3]overlay=x='min(-w+(t*w/0.5)\,0)':shortest=1[vv2]; ^
[vv0][vv1][vv2]concat=n=3:v=1:a=0 [video]" -map "[video]" output.mp4