vars2 <- structure(list(test = "THIS_IS_A_TEST", page = 1:10, api_key = "1bad2c72-3a0e-4139-8f88-1c74217c2cc0", LL = c("AA", "BB", "CC")), .Names = c("test", "page", "api_key", "LL"))

vars3 <- vars2

lapply_do.call <- quote({
    vars <- vars3    
    vars <- lapply(names(vars), function(nm) paste(nm, unlist(vars[nm]), sep="="))
    do.call(paste, args=c(vars, sep="&"))
})


sapply_apply <- quote({
    vars <- vars3    
    vars <- sapply(names(vars), function(nm) paste(nm, unlist(vars[nm]), sep="="))
    apply(vars, 1, paste, collapse="&")
})



identical(eval(lapply_do.call), eval(sapply_apply))

microbenchmark::microbenchmark(eval(lapply_do.call), eval(sapply_apply), times=150L)
#   Unit: microseconds
#                     expr      min       lq   median       uq       max
#   1 eval(lapply_do.call)  630.573  653.367  671.056  723.253  1280.578
#   2   eval(sapply_apply) 1177.432 1229.348 1265.001 1382.547 15483.745