So, for anyone following this odyssey with bated breathe:
1. Woocommerce Memberships $150 plugin was slowing down my site speed significantly once I added my membership plans. I uninstalled.
2. Instead, I installed too excellent plugins for what I needed (which was to provide membership level discounts on different product categories to different types of members). One was the free Members plugin (https://wordpress.org/plugins/members/). This allowed me to create different roles for each of my different members on the backend. When folks purchase a membership (ours are free), we then manually assign them a role. Not actually a bad thing – I noticed with the other plugin that if you deleted your old orders, ALL OF YOUR MEMBERSHIPS DISAPPEARED!!! Not so with this system. Anyway, then, using Pricing Deals for Woocommerce https://wordpress.org/plugins/pricing-deals-for-woocommerce/ (premium version), I could assign the discounts to different membership levels for different products. Voila. No site speed issues.
Thank you to the kind folks at Swift Themes for their patience and help as I worked through this incredibly frustrating issue!