yes, slow running can effect runners. sometimes the form of the runner becomes poor when running at a slower pace. working on good form and avoiding too much rotation of the hips as well as foot placement which leads to over-pronation.
rather shorten the runs until becoming stronger. doing less is better to start with. these programs are aimed at progressive training, hence why you only meant to do the build-up after being on a few cycles
hope this helps, however not easy when not seeing how the person runs