"大量使用标语" can be translated into English as "extensive use of slogans" or "heavy reliance on slogans", depending on the context and the nuance you want to convey.
"Extensive use of slogans" emphasizes the widespread or frequent application of slogans.
"Heavy reliance on slogans" suggests a strong dependence or overemphasis on slogans, possibly implying that they are being used as a primary or perhaps overused tool.