fread takes a lof of memory when "skip" is large

You can use the ability of fread to accept a shell command that preprocesses the file as its input. Using this option we can run a gawk script to extract the required lines. Note you may need to install gawk if it is not already on your system (Linux and Unix-like machines usually have it already, on Windows you may need to install it).

n = 100   # lines to skip
cmd = paste0('gawk "NR > ', n, '" ', filename)
lines = fread(cmd, nrows = rowPerRead)