What's the highest marginal tax bracket (federal) in the US? By the time Hendrik's career is over he'll have made like $66M including this full amount. If he has even half of that invested, $30M making only 1 point per year = $300,000 in annual income for him. In Canada anything above $220,000 is taxed at the highest level.
Point is that maybe all of the $15M would be taxed at the highest level regardless of whether he gets it at once or over 10 years. This might be different if Hendriks mismanages his money and the $1.5M / year is his only income, then I guess he would save a bit of tax (but the amount is probably not huge - your talking about a few points of difference on a few hundred thousand dollars). This might also change a bit if he can do annual income splitting with a spouse who doesn't make much/anything.
Even if there are small taxation benefits to receiving the money over time the benefits of getting it all up front would blow those savings out of the water, unless Hendriks puts it all in a WNBA team or something and takes a some big losses.