The mass that the falcon heavy can send to TLI is ~16t.

That number sounds too optimistic to me.

You start off with 53000kg in LEO. Assuming a semi-major axis for the TLI orbit of 200000km (about half the lunar SMA), and starting with a 200km LEO staging orbit, we get 3133 m/s of delta-V for the TLI.

Assuming an Isp of 338s or 3315.78m/s, we get a mass ratio of 2.5725. Now, how much payload you get depends on the dry weight of the third stage. Assuming 5000kg dry weight and 2000kg residuals, we get a mass to TLI of

(53000kg+7000kg)*1/2.57-7000kg=16324.33kg

I think these are pretty conservative numbers for dry weight and residuals. Now, the big question is if they can really make 53t to LEO, but on that we just have to take their word.