I think we're looking at this the wrong way.
If the A380 is departing you'll be placed 15 miles behind the preceding.
If however you can swap to an RNAV without too much hassle then you'll knock 7 miles off your approach/delay BUT you do NOT have to accept the RNAV if there is any concern it's going to overload the flight deck.
If it makes you uncomfortable enough to have a "moan" on here then please decline the RNAV - it's not an instruction it's an invitation!
30W, I'm pretty sure the ATIS would not give "expect RNAV approach" to accommodate the A380 departure. I suspect the ILS was off for another reason.
Ps. There's nothing quite like a 15 mile gap for reducing workload.