You really need to use PCP for 48 months and a larger deposit to gain the benefit with Tesla, for your 15k/year example the PCP and loan are both £743/month with a £10k deposit and the PCP monthly figure goes down slightly more if that's increased because the GFV doesn't change with larger deposits.
As usual with finance you have to look at your own numbers and requirements then decide what is the better option for you in each individual case. Tesla are a little odd in that they offer significantly different interest rates for PCP and Loan and their GFVs seem pretty conservative (almost £10k less than other manufacturers would set for a similarly priced vehicle).
I agree with you about lease though, for private customers it really feels like the monthly numbers are way too high.
For some reason, on a three PCP deal, which I favour (I've also stopped buying green bananas) the max deposit Tesla allow on a £61, 590 cash price is £18,447. Also, 10,000 per month is the minimum mileage for their calculations. Also, the residual/final payment is quite low at 3 years namely £25,250 which means the monthly payment is £636.
Back in the day when HP for cars was still fairly novel, people were just so keen to get the motor that they did not give much thought to the (flat) interest rates. The important bit was the monthly payments which were never advertised with the cars - as one sees nowadays.
So, the dealer, after a a short battle ( "are you trying to bankrupt me sir") would give in to the customers' sale price negotiations if he knew they were financing through him. He would then quote the monthly payment and the customer would sign the agreement. In fact, the dealer would have calculated a repayment which would generate a settlement from the HP company equal or more than the original sticker price).
Having said that, I have been a cash buyer for many years and have found this current exercise quite interesting. Leasing, for retired private individuals, seems a bit of a mugs game. However, although flat and APR rates are quoted for the PCP deals, I can't make the numbers agree with the rates/periods. So, I guess it's never changed in its opacity, except maybe for C.A.s and the initiated, although regarding the latter, I am not sure the sales agents understand how "computer" arrives at the numbers.
Therefore, go compare, in the generic sense, and choose what seems closest to your needs because.... it is what it is!