I think what @TopTier was trying to tell you was that transferring from a Korean university or starting undergraduate studies in the U.S. would amount in similar time (both 11-12 years), but transferring is just more difficult.
Some colleges will have lower rates of acceptance for underclassmen transfers (freshmen and sophomore) and some just have very little room for 4-year transfers, let alone international. You could have a better shot if you applied as an incoming Freshmen.
So basically, the “easiest” (time-wise as you mentioned) route would be to:
- Apply to colleges in the U.S. as an incoming freshmen
- Earn a bachelor’s degree (focus your studies on Bio, Chem, Math, Physics, Social/Behavioral Sciences)
- Take the MCAT
- Apply to graduate schools