BT are using EE's network, so the agreement will include the limits as you describe. Most (if not all) MVNO arrangements will be set up such that the 'parent' network have the better service levels, be that in terms of priority or data speeds.
I would hope this will change when/if BT complete the purchase of EE.
In practical terms the limits on data you mention will be of negligible importance. On a mobile device, what can't you do at 30/15 that you can do at double plus? Very little.