It's easier to get to the tube from T5 than T3! It's literally straight down by lift rather than the long walk at T3.
The only issue to bear in mind is that there are fewer trains (so a longer wait) from T5 than T3 but I wouldn't worry about that.
If you have lugagge then it will actually be easier to change to the District line at Hammersmith or Barons Court to Embankment then it's a short straight walk up to Charing X (I also think it's possible to take a lift / escalator up to the Jubilee bridge level and walk into the station that way rather than walk up the Villiers Street slope) Not sure what the step free options are at Leicester Square - check the TFL website.
You could always switch to the Northern line at Leicester Square down to Charing X rather than walk the streets.