IT dept says I have enough memory/RAM/graphics card etc but an instagram video of 15 min length still has audio lagging in both programs. I am trying to add a few captions and end credits - very simple. How do I stop the audio lagging? Thanks
I don't know if I have ever seen a system powerful enough to playback a 15-minute composition in real-time. If the 15-minute shot is dynamically linked to a Premiere Pro sequence, you'll have to render the preview in Premiere Pro to have it playback in real-time. After Effects is not an NLE. Every pixel on every layer and every effect, blend mode, transformation, and layer style must be rendered before it can be previewed. That takes time and system resources. Premiere Pro (and all NLEs) play video streams, usually at a lower resolution, until you get so many layers and effects that the streams must be rendered to play back smoothly.
If your AE Comp is one shot and 15 minutes, you'll have to render it. If it is multiple shots with cuts or transitions, you'll be better off breaking it into one-shot segments, rendering it, and doing the final editing in an NLE.
No offense, your IT doesn't seem to understand how AE nor Premiere works just like you have wrong expectations. You can make AE slow to a crawl even on the most poweerful system if you don't configure it suitably. It's all about settings and using the correct methodology as Rick already hinted at. It's unlikely that a Dynamic Link project wil lever play in realtime bar the most basic video being in it with no effects. Anyway, more info about actual settings, your system, your project contents is needed.