As you must realize, you have defined t_salesf_Lead to be a set with
about 2^50 elements. TLC cannot enumerate the elements of such a big
set. It can be hard to use a set in a spec in such a way that TLC
doesn't have to enumerate it. You can ensure that TLC doesn't have to
enumerate the set S by not defining S, and instead defining an
operator InS where InS(x) is true iff x \in S.
In your example, you can define the following, where I have
abbreviated t_salesf_Lead as TSFL.
[ Id |-> d_lead_id,
IsDeleted |-> d_not_used,
MasterRecordId |-> d_not_used,
TSFL_Fields == DOMAIN TSFL_Domains
/\ DOMAIN x = TSFL_Fields
/\ \A f \in TSFL_Fields :
x[f] \in TSFL_Domains[f]
(Note: If you want to write proofs, you'll need to add to the
definition of InTSFL(x) a conjunction asserting that x is a function.
However, this definition works for TLC because TLC will report an
error in evaluating InTSFL(e) if e is not a function.)
If you can write your spec using InTSFL rather than TSFL, then this
will solve your problem. Otherwise, you will not be able to use TLC
to check the spec.