There's a lot of guess work in there rob. Nobody knows, yet, what interest rate they will be paying or over what period the money will be repaid but it certainly won't save Arsenal £20m per year. SwissRamble done a thread on twitter and his best guess, assuming a much lower interest rate & the debt being refinanced over a much longer term, would save Arsenal approx £5m in interest and £5m in repayments
There is the potential for a nasty surprise here too. Kroenke borrowed £500m to buyout Usmanov, which is due to be repaid next month. SwissRamble speculates that this £200m odd could be rolled into a much larger refinance along with the other £500m. Will Arsenal then just pay the interest on the £200m stadium debt or will they end up paying for the pleasure of being owned by Kroenke too?