Relying on the tyres that you currently have for both size and load rating is risky. There's absolutely no guarantee that they are what you need.
However, 215/65/16 is fine for standard 16 wheels, albeit a fraction wider and therefore slightly taller than stock which is 205/65/16. Are they all the same? (It wouldn't be the first time...) What are the sizes on the sticker behind your door?
What gross weight is you van? Ie. T28, T30 or T32? This is an important consideration for tyres as different (minimum) load raings are required. This, in itself, can affect tyre availability but, at that size it's probably not a massive issue.
For front and rear wheels and tyres of the same size and type, 10 - 15mm spacing seems to be the sweet spot to make them sit the arches equally. However, there is more to spacing than simply asking for a width. You will need longer bolts (as mentioned above) to account for the extra material but these will also need to be of the same design and obviously the same thread. There are a few common bolt seat types such as ball/radius, taper/cone and flat and using the wrong type can be catastrophic. Similarly, the spacers can also be of differing designs such as hubcentric, lugcentric and bolt on. You're unlikely to find bolt on spacers for 10-15mm so, in this case, hubcentric is your best bet and only sensible option. These are designed to mimic the centre bore of your wheels to centralise the spacer on the hub spigot. They will usually also replicate the spigot on their outer face to ensure your wheels are centred. Obviously, these need to be matched to the sizes of your wheels and hubs.
Finally, some insurance companies do ask if you have spacers fitted. It may not affect your premium and I would be interested to know if a claim has ever been denied because of spacers (at sensible widths). That part is up to you.
So, you could ask the tyre fitter to fit some spacers but, I would do a little more research first to make sure that you know what you want and need.
, if you're loathe to fit lower suspension and staggered wheels you could always go the swamper route and fit off road balloon tyres on your stock wheels?
