You don't need to register in every state where you have CLIENTS — you need to register in states where you're "transacting business." The definition varies by state, but generally:
Requires registration: Having an office or employees in the state, owning/leasing real property, regularly meeting with clients in-person in the state, maintaining inventory there.
Usually doesn't require registration: Having customers who happen to be in the state, remote service delivery, occasional travel for meetings, maintaining a bank account.
Consequences of not registering: (1) Can't use state courts to enforce contracts against clients in that state, (2) potential fines and back fees if caught, (3) some states impose penalties on the entity and personal liability on managers.
For a remote consulting business serving clients in 15 states, you likely only need to register in states where you have physical presence — your home state (if different from WY) and any state where you have an office or regularly work in-person. The others probably don't trigger registration requirements for remote services.