Depends which model you really want, but I'd say hang fire, you'll get far more discount on a T6 than you've been offered, especially as the 6.1 launch date nears.
The dealer network will have various sales objectives to meet with the current model and that traditionally proves difficult to achieve when a new model is on the horizon. Prospective buyers will hold off until the new one arrives, but the network will still need to shift their unsold T6 model allocation in the meantime, which means they'll offer buyer's far greater discounts as the launch date approaches.
Now is the time to negotiate with the dealer network for the biggest discount. They don't want unsold T6 dealer allocations on their books now that they have the new T6.1 on its way so now is the time to hit them.
If your local dealer won't play ball call another dealer, and so on. You'll soon land on a dealer who has to clear the decks in readiness for the new model and will therefore be more willing to offer you a significantly greater discount. Start with the big city dealerships, they typically have the largest sales targets to meet and will be in a better position to accept a below-the-belt offer than the rest of the network would.
As a final bit of advice, play the Brexit thing to your advantage. New car and van sales are significantly down against this period a year ago, due to Brexit uncertainty. However, the sausage machine is still churning out the T6s and buyers still need to buy them or else there'll be a log-jam at the factory and, ultimately, the dealer network. That's likely to be happening now. Remember that. It could be the difference between a little bit of discount, or a massive amount.
The same apples to the 6.1. The network need to meet their sales objectives, which are invariably more than the previous year, against a climate of falling sales and future uncertainty. Believe me, the VW network is more receptive to offering greater discounts now than this time a year ago so do your research and be sure to check out more than a couple of dealers.
Good luck.