According to @BitMEXResearch, four rounds of spam attacks on the Bitcoin network in 2015 significantly disrupted user experience, particularly during the third attack from July 7 to July 11, 2015. The increased on-chain congestion led to delayed transactions and higher fees, directly affecting traders and payment processors who relied on timely confirmations. These disruptions underscored the importance of scaling solutions for Bitcoin and highlighted transaction fee volatility as a crucial factor for crypto trading strategies at the time (Source: BitMEX Research blog).