I often compare tires at the Miata Tire Size Calculator that can be located via Google.
A 215/65/15 is different enough from the original 205/75/15 that I'd personally avoid it. It's 4.1% off, so when the speedometer reads 60 the vehicle is travelling 57.6.
If a 235 section width will fit under the van, a 235/65/15 is only off by 0.3%, so when the speedo reads 60 you're going 59.8. I don't know if that wide of a tire will fit one of these minivans though, as it's about an inch and an eighth wider.
215/70R15 might be better, or consider moving to 16 inch wheels and tires. You could pull a set from a 01-07 model van and be all set. I like these myself:
Those vans used 215/65R16 tires. 27 inch diameter compared to 27.1 inch on your 205/75R15's. Not bad at all, should fit fine.
You can also just use the 16 inch steel wheels and grab a set of hubcaps. Your hubcaps won't fit the 16 inch wheels. If you have alloy wheels you could sell them after you get the 16s. Ride quality won't suffer much if at all from the wheel size change, just make sure you pick a strong tire to go on. I'll heartily recommend you ignore any S or T speed rated tire. Get an H rated tire, doesn't have to be a performance tire, touring and grand touring tires are in H and even V speed ratings and they're great. Yokohama Avid Ascent is the one with the highest UTQG trweadwear number in that size (and is only a $94 tire on TireRack). The Yokohama Avid EnVigor, Kumho KH18, andKumho Solus KL21 are right behind that.
Another thing, newer 01-07 base and SE model vans used 215/70R15 tires which are basically the same as 205/75R15. Shouldn't rub.
I'm running P215-R70-15 Goodyear Viva 1 tires from Walmart on my 94 GC without any problems except that Walmart would not install the wheels on the van but did install the tires on the wheels. That was no problem as I had a set of aluminum wheels I bought on eBay and installed the wheels myself. Just my $0.02.
When I bought our 98 GC, I did three things: I put stainless steel,teflon lined brake lines on it , threw away the oe pads and shoes to be replaced with semi-metallic parts and I bought 4 new tires, 225/60/16 size.
I had aluminum rims to start with but found several sets at a local wrecker for less than $200, clean and straight.
The brakes on these vans need all the help they can get and the stainless lines with the semi-met pads and shoes eliminated all soft pedal issues, the tires made it safer to drive and felt much more "planted " than the OE 215/65/16 pos tires.
Currently over 350 K and no issues.