I asked Dan O’brien what he did to overcome some of his 1500m struggles because over the last two years I have had them too. He said something that helped him was doing a time trial about every 3 weeks starting with about 700m the first week and building up to about 1200m. During those, run whatever pace your goal is for the 1500m. I haven’t had a chance to start trying it myself, but I plan on doing it over the summer to test it out for myself and for my athletes to do next year. The reasoning for it was more mental than physical, but if you try it out let me know how it goes.