The Methodist movement began in the 18th century as an open-air revival, peak low church, led by an Anglican professor at Oxford (assumptively peak high church). Low church and high church refer to liturgical styles or styles of worship. A high church service has all the smells and bells, incense, sitting and standing and recitation of texts. Usually the worship leaders are dressed in special garbs for the occasion (with fun words like 'chaucible').
Low church, in contrast, is exemplified by the tent revival, with extemporaneous prayers and sermons and speaking in tongues. Informality reigns supreme. In Article XIV, we see the church positioned against the Church in Rome. That article should be read from an ecumenical with an understanding of the anti-Catholic sentiments that were to be found in the 16th and 18th centuries in England. Likewise, We should understand article 15 against the speaking in tongues without a translator as not referring to any practice analogous to modern day Pentecostalism or charismatic churches. Article 15, instead, points to 1 Corinthians 14 and Paul's extended reflection on prophecy and the speaking of tongues. What Paul emphasizes is that all spiritual gifts must be for the upbuilding of the community. If they are solely for individuals, they are no longer truly spiritual. This is why it is important to have translators to speaking in tongues so that any spiritual insight is not limited to any one individual but to the whole church.
For us today, whether we practice speaking in tongues or not, the lesson of 1 Corinthians 14 (and of Article 15) is that our gifts of the Spirit must be used for the upbuilding of others. They cannot be hoarded. It is like the parable of the talents. To those who use many, much will be given, to those who bury their talents out of fear that they will have even those taken away from them.
Or as the old children song goes,
This little light of mine, I’m going to let it shine.
We must let our gifts shine, whatever they may be. When we hide them or only use them in ways we understand, we have already received our reward.
Article XV — Of Speaking in the Congregation in Such a Tongue as the People Understand
It is a thing plainly repugnant to the Word of God, and the custom of the primitive church, to have public prayer in the church, or to minister the Sacraments, in a tongue not understood by the people.